1. Field of the Invention
The present invention relates to a socket that can be attached to a motherboard and be mated with an integrated circuit package.
2. Background Information
Integrated circuits are typically assembled into packages that are mounted to a printed circuit board. The printed circuit board may be a motherboard of a computer. The integrated circuit package can be plugged into a socket mounted to the motherboard. The socket typically has a plurality of contacts that are soldered to the motherboard and which can receive corresponding pins of the integrated circuit package. The socket contacts may be solder balls that are soldered to corresponding surface pads of the motherboard. Surface mount solder ball interconnects are preferred when integrated circuit packages are to be soldered to both sides of the motherboard. Additionally, surface mounting increases the routing density of the board. The integrated circuit package is plugged into the motherboard by inserting the pins of the package into the contacts of the socket.
The contacts are integrated into a dielectric base of the socket. The base is typically constructed from a molded fiber filled resin material. The fibers typically become aligned in the direction of flow during the molding process. The resultant socket may have a non-uniform coefficient of thermal expansion ("CTE"). For example, when a liquid crystal polymer ("LCP") resin is employed the socket may have a CTE of 10-15 parts per million per degrees centigrade ("ppm/.degree. C.") in the direction that the fibers are oriented, and a CTE of 50-60 ppm/.degree. C. in a direction normal to the fiber orientation. The motherboard may be constructed from a material that has a CTE of 15-17 ppm/.degree. C. Variations in temperature will cause the socket to expand/contract at a different rate than the motherboard particularly in the direction normal to the fiber orientation. The differential expansion may cause failures at the solder joints of the motherboard and socket contacts.
Some sockets contain a mineral filler to minimize the CTE in the cross flow direction. The mineral filler is difficult to mold and increases the cost of producing the socket. There have also been attempts at integrating stress relief holes in the socket, but such a solution reduces the structural integrity of the part. It would be desirable to reduce the thermal expansion of an integrated circuit socket in the direction normal to fiber orientation without significantly increasing the cost or reducing the structural integrity of the socket.
The socket is typically molded by injecting the resin through a gate. The resin will typically flow from the gate in a radial manner. The radial flow creates a non-uniform CTE throughout the socket. It would be desirable to provide a socket that will increase the uniformity and predictability of the CTE throughout the socket.